In recent years, dramatic advances have been made in the development of lightweight, compact mechanisms for correcting common and debilitating injuries to body joints such as fingers, wrists, knees, elbows and the like. Perhaps the greatest advances have been made in the design of orthotic brace units which counteract instabilities in a joint by reinforcing the joint as a whole to prevent unwanted motion. Such orthotic devices are typically formed with a mechanical joint supported by a pair of bracing members. The mechanical joint is defined by a pair of side bars, each of which has a hinge-like pivoting joint in its middle with the top and bottom ends of the side bars being connected to bracing members which fit around a body portion above and below the joint to be supported. These devices operate generally by confining the movement of the joint as it bends so that unwanted motions are eliminated or at least minimized. The most commonly known orthoses are orthotic knee braces of the type commonly used by athletes who have suffered injuries to either the ligaments that interconnect the lower femur and upper tibia, or to the bones themselves, which result in knee instabilities.
Joint instability is not the only debilitating condition of a body joint which requires correction. The operation of a body joint may be impaired in a manner which inhibits the operation of the joint in accomplishing extension or flexion. For example, a flexion contracture prevents full extension of the joint, while an extension contracture prevents the joint from being bent or flexed to the full extent. Obviously, the treatment of a flexion contracture or an extension contracture requires more than the mere support against instability provided by many conventional orthotic devices.
To treat flexion and extension contractures, spring-biased splint units have been developed to provide a force across a body joint. These splint devices provide tension which operates in opposition to a flexion or extension contracture and thereby not only provide support in instances where muscular weakness exists, but also enhance rehabilitation. One type of known adjustable spring-loaded splint includes a pair of lower struts and a pair of upper struts of tubular configuration which are pivotally interconnected. Spring biasing units mounted within the tubular struts are adapted to apply an adjustable force at the pivot point which tends to align the two pivoted struts. Such an adjustable splint mechanism is illustrated by U.S. Pat. Nos. 4,397,308; 4,485,808; 4,508,111; 4,538,600 and 4,657,000 to George R. Hepburn.
Although known adjustable splints operate effectively to apply tension across a joint, they are relatively heavy and bulky and consequently impede to some extent free activity at the affected joint. The heavy tubular strut assemblies used in prior art splints are generally not coextensive from the connecting pivot point, and thus may be brought into only parallel rather than axially aligned relationship. It is impossible to contour these heavy struts to conform to the limb of a user, and the degree of pivotal movement within which the applied force is linear is generally small. Such splints generally use straight line springing against a cam. The rotational force applied by the cam is extremely non-linear due to the changing moment arm on the cam surface. This variation prevents the application of a constant therapeutic force and requires constant adjustment to the spring force through the desired range of motion.
Finally, with known prior art adjustable splints, the bias adjustment mechanism for the splint is difficult to reach, and the degree of adjustment is often difficult to ascertain. Accurate adjustment of the bias for such prior art units with the splint in place is not easily accomplished, and the bias structure employed does not facilitate polycentric joint structures of the type better suited to the motion of certain joints, such as the knee.
In general, prior art splints have been constructed for force application in either a flexion or contraction direction, but not both. However, U.S. Pat. No. 4,370,977 to Mauldin shows a knee brace with a spring connected to a hinge member which may be used to resist motion in either direction. Resistance in one direction is transformed to resistance in the opposite direction by removing a thumbscrew and the torsion spring, and reinstalling the torsion spring in different holes on the hinge portion. However, mechanisms of this type do not provide an even adjustment of force capability, and reversing the direction of force application requires complexity in the operations required to reverse the device.
U.S. Pat. No. 5,052,379 to Airy et at. shows a brace with frame sections connected by a pivot joint which resists relative movement of the frame sections in either or both directions about the pivot axis. A removably connected torsion spring provides the resistive force. This reference, however, uses different torsion springs to impose the resistance desired, rather than changing the position of a single torsion spring.